Electrolytic reduction of nitro or other compounds.



No. 700,670. Patented May 20, I902.

m. 'BUCHNER.

ELEGT ROLY TIC. REDUCTlON'OF NITRQ OR OTHER COMPOUNDS.

' (Application filed Nov. 10, 1899.)

(No Model.)

m: NORRIS Fergus cu. ypqovo-Lufnou summon/u. a

UNlTED I STATES PATENT OFF-ICE.

lVIAX BUCHNER, OF MANNI-IEIM, GERMANY, ASSIGNOR TO THE FIRM OF C. F.

BOEIIRINGER & SOEHNE, OF MANNHEIM-WALDHOF, GERMANY.

ELECTROLYTIC REDUCTION OF NITRO OR OTHER COMPOUNDS.

SPECIFICATION forming part of Letters Patent No. 700,670, dated May 20, 1902.

Application filed November 18, 1899.

To all whmn it ntrty concern.-

Be it known that I, MAX BUOHNER, a citizen of the Empire of Germany, residing at Mannheim, in the German Empire, have invented certain new and useful Improvements in Electrolytic Reduction of Nitro or other Compounds; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to. make and use the same.

This invention relates to the art of red uction, and in particular to the art of reducing nitro compounds to form the corresponding amins. Hitherto it has not been possible to readily accomplish such reduction by electrolytic methods and without waste and the formation of side products. This appears, 6. from the numerous experiments of I-Iaussermann, Elbs, Gattermann, Noyes & Clement, Voigt, Loeb, and others. (See the compilation given inHaber, Techm'schc E1615 trochemie, page 522.) Thus, e. g., it has been found on reducing nitrobenzene, which has hitherto been studied most exhaustively, that according to the solvent employed (such as concentrated sulfuric acid, dilute or alcoholic solution of sulfuric acid, concentrated hydrochloric acid, or acetic acid) or the material of the cathode (such as platinum, lead, orvzinc,) final products consisting of varying quanti ties of anilin, benzidin, paraamidophenol, paraamidophenol sulfo-acid or anilin chlorid would be obtained.

A uniform unvarying and certain reduc-' tion of nitrobenzene to anilin by means of electrolysis has never been attained by any of the methods hitherto employed.

It is the object of this invention to overcome the difficulties thus set forth, said in vention being based 011 the discovery which I have made that nitro compounds of the arcmatic as well as the fatty class may be reduced to the corresponding amins if the same are dissolved or suspended in a suitable bath, such as water or an alcoholic aqueous solution of hydrochloric acid, and submitted to the action of an electric current in the oathode-chamber of an electrolytic cell or battery in the presence of tin. Moreover, I have found that under such conditions the yield will be almost theoretical. For this purpose Serial No. 737,494- (No specimens.)

I may employ either a tin cathode directly or an indifferent ca'thodesuch as, e. 9., a platinum, lead, carbon, or nickel cathodetogether with a cathode electrolyte to which has been added a small quantity of a tin salt, such as stannous chlorid.

Underthe method devised by me as based on my discovery when a cathode consisting of metallic tin is employed the tin will continue to go into solution so long as any unchanged nitro compound is present, the nitro compound being simultaneously reduced;

but such dissolved tin will be immediately such, 6. g. as a cathode of nickelis employed and chlorid of tin is added to the electrolytic fluid in the cathode-space, metallic tin is first separated and deposited on the nickel cathode, which thereafter will actlike a pure-tin cathode in the manner above set forth. It will be seen, therefore, that under this process' a migration of positively-charged tin ions from the cathode into the cathode electrolyte takes place under conditions whereby the current is caused to simultaneously deposit tiu ions at the same place.

Under my invention I am therefore onabled to reduce any desired quantity of a nitro compound to the corresponding amin with the aid of a very small quantity 'of tin, as I will show in Example l below.

In reducing, e. g., nitrobenzene to anilin it is therefore not necessary that an amount of tin equivalent to the amount of anilin produced is taken up by the electrolyte permanently and without being again separated by the current.

My method of reduction enables me to employ currents of high density and up to eighteen hundred amperes per square meter, so that the reduction may be carried out very rapidly. It is necessary to cool the'cathodespace in order to avoid toojintense heating.

When the reduction is carried out correctly according to my invention, the evolution of hydrogen will not be observed until almost the entire quantity of the nitro compound under treatment has been reduced, and after the completion of said reduction no tin will be found in the cathode-bath, so that it is rendered possible to obtain the resultant bases in the form of their chlorids direct-1y and in a pure condition.

It is to be understood that the metallic tin is the direct and primary vehicle or agent of the reducing process; the function of the current is merely to precipitate the tin. In other words, the reduction of the compounds to be reduced is not effected by causing the current to act upon them, but by the fact that the current acts upon the tin containing cathode-electrolyte, whereby the tin ions are discharged at the cathode and separated in the form of metallic tin. This metallic tin is, however, speedily and continuously redissolved in the electrolyte so long as any unreduced compound capable of being reduced to an amin remains in the acid cathode-electrolyte. Where we start with a tin cathode and without tin dissolved in the cathode-electrolyte, the tin from the cathode will rapidly go into solution so long as the electrolyte contains the reducible compound. From the acid electrolyte,which thus contains dissolved tin and the resultant amin, there will be immediately precipitated metallic tin without evolution of hydrogen in the presence of highdensity currents, such tin being again dissolved, and so on, the cycle of reactions being repeated until no more reducible compound is left in the electrolyte.

My invention accordingly consists in subjecting nitro compounds to the action of an electric current in the cathode-space and in the presence of tin, the tin being either the material of the cathode or in solution in the electrolyte; and my invention consists in such further features, details, and methods as will be hereinafter described, and pointed out in the claims.

I will now give a detailed description of the preferred manner in which I carry out my invention. For this purpose I have selected the following examples:

Example 1 -Reclztciion of Nilrobeneene f0 Am Z in.

(a) Employment ofa 25m ccltho(le.-An electrolytic cell is divided into an anode and a cathode space by means of a suitable and convenient diaphragm. Into the former is poured sulfuric acid of thirty-per-cent. strength, and an anode of indifferent material is arranged therein. The cathode-space is preferably provided with a stirring appaand materials are in place, the reduction is effected by introducing an electric current of a density preferably of eighteen hundred amperes per square meter for a bath potential of 6.5 volts. The reduction takes place very energetically without the evolution of hydrogen. The attendant great development of heat is counteracted by thorough cooling, while the cathode-bath is at the same time maintained Well mixed by suitably stirring. When the reaction process is completed, hydrogen begins to escape regularly, and thereby the end of-the operation is indicated. The current is now out off, the colorless cathodebath is separated f rom the tin sponge or flakes suspended therein by filtration, and the filtrate is evaporated. The residue is anilin chlorid in the form of a colorles'crystalline mass, from which the anilin may be isolated by known methods.

(1)) Employment of an t'nd'ifi ere'nl cathode in the presence of Cb lin salt-The division of the electrolytic cell into an anode and a cathode space and the other arrangements of both ,spaces are the same as described under 1, with these exceptions: that no tin cathode but an indifierent cathode, consisting, for example, of a net of nickel wire, is arranged in the cathode-space and that two parts, by weight, of stannous chlorid are added to the cathode-bath, which consists of a mixture of twelve parts, by weight, of nitrobenzene with seventy-five parts, by volume, of fuming hydrochloric acid and fifty parts, by volume, of water. On introducing into this'electrolyte a current having a density of one thousand amperes per square meter for a bath potential of 8.5 volts metallic tin is first deposited on the nickel cathode, such deposited tin acting exactly like the tin cathode described.

under 1. As soon as the evolution of hydrogen begins, thereby indicating the complete reduction of the nitrobenzene in the cathode-bath, further quantities of nitrobenzene, together with the amount of hydrochloric acid necessary toform anilin chlorid from the same, may be added to the bath, such further addition being repeated and continued until the solution is enriched with anilin chlorid to such an extent that it will directly solidify to a crystalline mass on cooling.

Example 2--Recl-ucti0n of Parcmt'trotoluene to Pctralolut'clin.

1, excepting that the cathode-space is charged with a mixture of twenty parts, by weight, of

meta-dinitrobenzeue, two hundred andfifty parts, by volume, of rectified alcohol, (fine spirits,) and one hundred and fifty parts,.by volume, of fuming hydrochloric acid.

Example 4-Reduction of AZ ;hct-Nitronaphihctlin f0 AZphct-lVapht/zyZa m'i'n.

Here, too, the process described under Example l is followed, with the exception that the cathode-bath consists of a mixture of twenty parts, by weight, of alpha-nitronaphthalin, two hundred and seventy parts, by volume, of rectified alcohol, (fine spirits,) and fifty parts, by volume, of fuming hydrochloric acid.

Example 5Reclu ciion of Phenyhtz'fromctha-ne 20 Bcnzylamin.

For this purpose the method set forth under Example 1 is carried out, with the'eXception that the cathode-space is charged with a mixture of five parts, by weight, of phcnylnitromethane, one hundred parts, by volume, of rectified alcohol, (fine spirits,) and two hundred parts, by volume, of fuming hydrochloric acid.

It will be seen from a review of all the examples above given in illustration of my invention that the same, broadly considered, consistsin submitting a substance to be reduced, such as a nitro compound, to the action of an electric current in the cathodespace in the presence of tin, by which I mean that said action takes place either in the presence of a tin cathode or of an indifferent or neutral cathode combined with an electrolytic solution of tin or of a tin salt.

It should be noted that in the above examples there is always present a tin cathode, since the indifierent cathode, as seen above, soon becomes coated with tin from the electrolyte solution. Therefore, though in one case we start with a tin cathode and a solution containing no tin salt or compound and in the second case with an indifferent cathode and a solution containing tin in the form of a compound or salt of tin, in both cases the current acts on the body to be reduced in the presence of a tin cathode.

The process described is hence essentially the same whether we start the reducing process with a tin cathode or with another cathode and an electrolyte containinga tin salt. The course of the reduction is identical for both cases.

The process of the electrolysis consists in the electric neutralization of the ions at the electrodes. In thus giving up their electric charges the ions become converted into free atoms or molecules, in which form they are capable of chemical reaction. At the moment of neutralization the ions may react upon one another or they may react upon other substances contained in the electrolyte. The former process is termec primary, the latter secondary.

All electrolytic reductions are instances of secondary reaction, both when the cathode employed is of indifferent material or when it is of material itself capable of reaction with the electrolyte. In the case of an indifierent cathode the hydrogen ions give up their positive charge directly to such cathode. In the other case the hydrogen ions give up their charge to the cathode material, (in the present case tin,) the metal of the latter continuously passing into the ionized state by solution in the acid electrolyte. The ions thereupon give up the charge received from the hydrogen ions to the cathode. In either case it is the hydrogen which, being electrically neutralized by the current, reduces the nitro group. The tin employed inthis reaction is continually redeposited after being dissolved.

The following electrochemical equations will afford an insi ht into the nature of the reactions when a tin cathode is employed:

is to be regarded as one of only momentary existence and has only been added for the sake of clearness. This combination of chemical reduction and electrolytic regeneration of the tin is a fundamental characteristic of my invention.

In the accompanying drawings I have represented one out of many possible forms of apparatus and electrolytic cells for carrying out the process involved in my invention.

In the drawings, A represents the anodechamber containing the anode-electrolyte, and a, the anode; O the cathode-chamber containing the cathode-electrolyte, and c the cathode, while (1 represents a diaphragm of any suitable material for separation of two electrolytes, as will be readily understood. S represents a suitable stirrer arranged within the cathode-electrolyte, the spindle or shaft s of which may be connected with any suitable source of power by a belt and pulley B P, as shown, or otherwise.

The cooling of the cathode-compartment may be carried out in any well-known manner, such as by cooling-coils and the like.

What I claim, and desire to secure by Letters Patent of the United States, is

1. The process of reduction which consists in introducing a substance capable of being reduced by tininto-an electrolyte capable of dissolving tin, and passing an electric current through the same in the presence of tin.

2. The process of reducing a nitro compound which consists in introducing such compound into an electrolyte capable of dissolving tin, and passing a current through the same in the presence of tin.

3. The process of reduction which consists in introducing a substance, capable of being reduced by tin into an electrolyte capable of dissolving tin, and passing an'electric current through the same in the presence of a tin cathode.

4. The process of reducing a nitro compound which consists in introducing such compound into an electrolyte capable of dissolving tin, and passing an electric current through the same in the presence of a tin cathode.

5. The process of reduction which consists in introducing a substance capable of being reduced by tin into a cathode-bath containing a compound of tin, and passing an electric current through said bath.

6. The process of reduction which consists in introducing a substance capable of being reduced by tin into an electrolyte capable of dissolving tin, and passing an electric current through the same in the presence of tin and at the same time stirring and cooling.

7. The process which consists in introducing a substance, which is reducible, and an amin into an acid electrolyte capable ofdissolving tin, and passing an electric current therethrough in the presence of a tin cathode.

8. The process which consists in introducing a substance which is reducible to an amin into an alcoholic acid electrolyte capable of dissolving tin and passing an electric current through the same in the presence of a tin cathode while stirring and cooling.

9. The process which consists in introducin ga nitro compound to be reduced into a cathode-bath containing hydrochloric acid and in which is arranged a tin cathode and passing an electric current through the bath.

10. The process which consists in introducing a nitro compound to be reduced into an alcoholic cathode bath containing hydrochloric acid, and in which is arranged a tin cathode, passing an electric current through said bath and stirring and cooling the same.

11. The process which consists in introducing a nitro compound into a bath containing a stannous compound and hydrochloric acid and having a cathode arranged therein and passing an electric current therethrough.

12. The process which consists in introducing a nitro compound into a cathode-bath containing hydrochloric acid and a stannous salt and having a cathode arranged therein, and passing an electric current therethrough while stirring and cooling.

In testimony whereof 'I affix my signature in presence of two Witnesses.

lVlAX BUOI-INER.

Witnesses:

JACOB ADR IAN, EDUARD KOBNER. 

